Advanced Engineering Tech - LS7 head On a 6.2 block.

What would keep you from running a ls7 head on a 4.07 bore 6.2 L Block?
Mocked it all up today and they seem to fit fine. Yes the chamber hangs over alittle,but nothing a little valve notching (.01-.020 max) wouldn't take care of.
I got a little over .040 clearence from the exhaust valve the the bore @4.062.
Intake has a mile atleast .200.
Anyone ever try this?
Thanks
Dave

I think they say valve shrouding. doesn’t matter what size valve but it wouldn’t be worth the benefit because of the shrouding. Kinda like running 4 inch exhaust on a 4 cylinder. It hurts more then it helps

I think they say valve shrouding. doesn’t matter what size valve but it wouldn’t be worth the benefit because of the shrouding. Kinda like running 4 inch exhaust on a 4 cylinder. It hurts more then it helps

Not everyone buys into this idea. Some folks have done quite well doing what the OP suggested. Other folks wouldn't consider it.

I think the idea has merit. It isn't a cheap thing to try, but the cost/hp might be not that unreasonable.

Jon

The whole reason i was thinking about it was, because i got a couple 6.2 block, a set of cnc ported ls7 heads,new 4.07 bore pistons(may need notching).
Thinkin about putting a stock crank, recon rods w/arps, hang pistons,throw a cam at it, and for less then $2000 Bang.
I guess my question is do you think they would out proform a set of ported l92.

The whole reason i was thinking about it was, because i got a couple 6.2 block, a set of cnc ported ls7 heads,new 4.07 bore pistons(may need notching).
Thinkin about putting a stock crank, recon rods w/arps, hang pistons,throw a cam at it, and for less then $2000 Bang.
I guess my question is do you think they would out proform a set of ported l92.

It depends on WHO ported your LS7 heads and WHO does the L92s...and of course the cam.

My guess is that stock OEM CNC LS7 heads with the correct valvetrain parts, the LS7 intake and the correct cam will outdo most of the ported L92 heads I've seen. The shorter LS7 intake runners will allow a higher power peak rpm if you are willing to spin it a little for power. The correct cam will also be driveable, if that's what you are after.

Keep thinkin' OTB.

Jon

did some measuring
Stock l92 heads and stock gm ported ls7
Clearence to the bore @~ .625 lift
LS7 (2.200 in 1.610 ex)
intake .120-.130
exhaust .040-.050

L92(2.160 in 1.60 ex)
intake .07-08
exhaust .070-.080

Dont it seem odd that the ls7 intake valve has more clearence.

And the shrouding is arguably only relevant at low lift numbers as once the valve is open the head is out of the way. Plus the exhaust is less sensitive to the intake on shrouding.

Correct me if I'm wrong but I think the LS7 heads have 12-degree valve angles whereas the L92 heads have 15-degree valve angles. Hence, maybe a little more room from a little flatter valve face.


did some measuring
Stock l92 heads and stock gm ported ls7
Clearence to the bore @~ .625 lift
LS7 (2.200 in 1.610 ex)
intake .120-.130
exhaust .040-.050

L92(2.160 in 1.60 ex)
intake .07-08
exhaust .070-.080

Dont it seem odd that the ls7 intake valve has more clearence.

Texas Speed had a set of PRC After market casting Ls7 style Heads for this very same set up....

I talked to them 4wks ago about it, They said stock bottom end Ls3 block w a Cam and There PRC 265cc, Small Bore Ls7 head made 600 CRANK HP,

But...The Trq Curve Sucked

He said w a Ls3 Storker 418/417 is what there where Really designed for

did some measuring
Stock l92 heads and stock gm ported ls7
Clearence to the bore @~ .625 lift
LS7 (2.200 in 1.610 ex)
intake .120-.130
exhaust .040-.050

L92(2.160 in 1.60 ex)
intake .07-08
exhaust .070-.080

Dont it seem odd that the ls7 intake valve has more clearence.

And we have a winner!!! Not sure how accurate the measurements are, but they give us an idea of what is going on here. This issue is precisely why L92 heads almost never perform how the flow numbers indicate that they will on paper. Also why GM came up with the LS7 port head for the Z06- the L92 fell short on so many accounts. Most aftermarket L92/LS3 port castings have valve centerlines that have been shifted in order to move the inlet valve away from the bore more like the LS7 head. Or you could offset dowel a factory L92 head to help this problem. In almost any form of racing they shrink the exhaust valve in order to allow for more intake valve. (There are other elements at work on the exhaust side which help evacuate the combustion pressure which alleviates the need to gain surface area with the valve).

Dont it seem odd that the ls7 intake valve has more clearence.

Not odd at all. They have different valve spacings.

The LS7 has the intake valve moved torward the center of the bore for a reason...

It stands to reason that if the measurments are accurate on a 4.062 bore then whos to say a .060 over 4" bore is out of the question. Is there any data on combustion chamber overhang onto the deck surface ?? And would this even be a issue to worry about ?? The difference is only .064/ = .032 around of deck surface (LS7 to 6.0).

So....with 2.20/1.61 valves and a 1.9685 spacing = 3.8735 total valve area (linear). Which gives a .0635 space between the valves.

Is anyone putting the LS7 on small bores, other than the 4.125 ???

Thanks.....